Inflatable member formed of liquid crystal polymeric material blend

ABSTRACT

A catheter having an inflatable member formed of a liquid crystal polymeric material. The inflatable member is formed from a blend of a minor amount, preferably less than 10%, of liquid crystal polymer with a major amount of a non-liquid crystal polymer having LCP fibers that are highly oriented in the machine direction. The aspect ratio of the liquid crystal polymeric material fibers is greater than 10, so that the polymer blend has mechanical characteristics similar to a fiber-reinforced composite with improved strength and optimal compliance.

BACKGROUND OF THE INVENTION

This invention relates to the field of intravascular catheters, and moreparticularly to an inflatable member formed in part of liquid crystalpolymeric material.

Balloon catheters generally comprise a catheter shaft with a inflatablemember on the distal end of the shaft, and are used in a number ofprocedures, such as percutaneous transluminal coronary angioplasty(PTCA). In PTCA the balloon catheter is used to restore free flow in aclogged coronary vessel. The catheter is maneuvered through thepatient's tortuous anatomy and into the patient's coronary anatomy untilthe inflatable member is properly positioned across the stenosis to bedilated. Once properly positioned, the inflatable member is inflatedwith liquid one or more times to a predetermined size at relatively highpressures (e.g. greater than 4 atm) to reopen the coronary passageway.

The material used to make the catheter inflatable member must havesufficient strength to contain the inflation fluid without bursting. Inaddition, the degree of compliance must be tailored so that theinflatable member expands during use, but does not overexpand and damagethe body lumen. During extrusion and subsequent processing of polymericinflatable member tubing, the longitudinal and radial orientation ofpolymeric molecules can be tailored to increase the longitudinal andradial strength of the inflatable member produced therefrom. Because theforce required to blow a inflatable member from tubing destroys some ofthe longitudinal orientation produced during extrusion, the extrusionprocess, and particularly the draw down ratio, is designed aroundoptimizing the molecular orientation that is ultimately produced in thefinished inflatable member. The strength of a inflatable member istypically expressed in terms of hoop strength and burst pressure.

Inflatable members formed from thermoplastics such as PET blended withliquid crystal polymers to improve the compliance of the inflatablemember have been suggested (U.S. Pat. No. 5,306,246 (Sahatjian et al.)).However, Sahatjian et al. fails to address the problem of lower burstpressures of inflatable members produced from blends of a minor amountof liquid crystal polymer with a major amount of a non-liquid crystalpolymer, relative to inflatable members produced from onlythermoplastics such as PET.

Therefore, what has been needed is a catheter with an inflatable memberhaving improved strength characteristics. The present inventionsatisfies these and other needs.

SUMMARY OF THE INVENTION

The invention is directed to a catheter which has an inflatable memberformed of a polymeric blend comprising a minor amount of a liquidcrystal polymeric material and a major amount of a non-liquid crystalpolymeric material. There are many suitable liquid crystal polymericmaterials that may be used, and a presently preferred example is VECTRAsold by Hoechst-Celanese. The non-liquid crystal polymeric material usedin the LCP blend may be any extrudable thermoplastic polymer, andpresently preferred examples are nylon 12 available from EMS, and PEBAXavailable from Atochem.

The LCP acts as reinforcement in the polymer matrix, similar to fiberreinforced composites, but at significantly lower dimensional scale andease of processing. One presently preferred embodiment of the inventionis a dilatation catheter which has an elongated catheter shaft and aninflatable dilatation member on a distal portion of the catheter.Conventional catheter design may be used, including over the wire, fixedwire and rapid exchange designs, having a single shaft with dual lumensor a multimembered shaft with inner and outer tubular members.

Liquid crystal polymers exhibit crystalline behavior in the liquidphase. The orientation of the molecules in the liquid state can bemaintained in the solid state due to the long relaxation times of thesemolecules. The molecular orientation improves the strength of apolymeric component in the direction of orientation. The extent ofmolecular orientation can be expressed in terms of the Herman'sorientation parameter (S) with a scale of from 0 (no orientation) to 1(very highly oriented), which is a factor of the draw-down ratio (i.e.the ratio of the diameter of the die to the diameter of the finishedextrudate) used during extrusion and viscosity. Liquid crystal polymerscan be made to solidify after extrusion with an even greater degree ofmolecular orientation than ordinary polymers, and thus can be used toform ultra high strength articles. However, the high molecularorientation may result in disadvantageous characteristics in aninflatable member, such as little ability to withstand loads appliedtransverse to the orientation direction, increased stiffness, and poorbonding between layers. These disadvantages are avoided by the polymerblend of the invention. In the polymer blend of the invention, theHerman's orientation parameter is about 0.5 or less. Thus, theinflatable member of the invention formed from a minor amount of liquidcrystal polymeric material existing as elongated liquid crystalpolymeric fibers having an aspect ratio of about 10 to about 100, andpreferably about 50 to about 100 has improved strength characteristics.

The inflatable member is formed from a blend comprising a minor amount,preferably less than about 20 to about 10 percent by weight of theblend, of liquid crystal polymeric material, with a major amount,preferably about 80 to about 90 percent by weight of the blend, of anon-liquid crystal polymeric material (hereafter, the LCP polymericblend). By blending the liquid crystal polymeric material with anotherthermoplastic material the transverse strength of the inflatable memberproduced therefrom is increased. Additionally, it has been found that aninflatable member having LCP fibers that are highly oriented in themachine direction has improved mechanical characteristics. Specifically,if the aspect ratio of the liquid crystal polymer fibers is greater than100, the LCP polymeric blend has mechanical characteristics similar to acontinuous long-fiber-reinforced composite. As a result, the main loadon the inflatable member is taken by the fibers (iso-strain process), asopposed to short fiber or dispersed phase composites where the load isshared by the filler and the matrix (iso-stress). Therefore, the LCPpolymeric blend having a high aspect ratio can be used to produce thinwalled inflatable members with improved burst pressures. Additionally,the risk of inflatable member overexpansion during use is reduced,because the high aspect ratio results in an advantageous reduction ininflatable member compliance.

An inflatable member formed from the LCP polymeric blend of theinvention has improved strength and optimal compliance due to the highaspect ratio produced during extrusion. These and other advantages ofthe invention will become more apparent from the following detaildescription of the invention and the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view partially in section of a inflatablemember catheter which embodies features of the invention.

FIG. 2 is a longitudinal cross-sectional view of the shaft of thecatheter shown in FIG. 1, in circle 2.

FIG. 3 is a transverse cross-sectional view of the shaft shown in FIG.2, taken along lines 3—3.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, the catheter 10 of the invention generally includesan elongated catheter shaft 11 with an inflatable member 12 on a distalportion of the catheter shaft which has an interior in fluidcommunication with a lumen within the shaft, and an adapter 13 mountedon the proximal end of the catheter shaft.

The catheter shaft 11 has an outer tubular member 14 and an innertubular member 15 disposed within the outer tubular member 14 anddefining with the outer tubular member 14 an annular lumen 16 which isin fluid communication with the interior of the inflatable member 12.The inner tubular member 15 has an inner lumen 17 extending thereinwhich is configured to slidably receive a guidewire 18 suitable foradvancement through a patient's coronary arteries. The distal end of theinflatable member 12 is sealingly secured to the distal end of the innertubular member 15 and the proximal end of the inflatable member 12 issecured to the distal end of the outer tubular member 16.

In the embodiment illustrated in FIG. 1, the outer tubular member 16 hasa relatively stiff proximal shaft section 20 tapering to a smallerdiameter and more flexible distal shaft section 21. The distal end ofthe proximal shaft section 20 is secured to the distal end of the distalshaft section 21 at lap joint 22 formed by suitable means such as heator laser fusion or commercially available cyanoacrylate adhesive.However, a variety of suitable configurations may be used to connect thedistal shaft section 21 to the proximal shaft section 20. The innertubular member 15 extends the length of the catheter and may be formedof suitable materials, including but not limited to polyethylene,HYTREL, or the like.

Inflatable member 12 is formed from a blend of a minor amount of aliquid crystal polymeric material and a major amount of an non-LCPpolymeric material (LCP polymeric blend). The LCP polymeric blend isextruded as tubing with high aspect ratio LCP fibers, which is thenprocessed into an inflatable member 12 using conventional procedures.The melt processed, e.g. extruded, LCP polymeric blend has a high aspectratio of about 10 to about 100, and preferably greater than about 50,and most preferably greater than about 80. In the extrusion process, ahigh draw down ratio and a viscosity ratio close to unity is used toproduce the high molecular orientation. The draw down ratio, as measuredby the outer diameter of the extrusion die divided by the outer diameterof the extruded tubing, is not less than about 2, preferably not lessthan about 3, and is typically about 3 to about 10. The viscosity ratiois not less than about 1.1, and is typically about 1.1 to about 3.0.Because the inflatable member is produced from extruded tubing having ahigh aspect ratio, the load during pressurization of the inflatablemember will be absorbed by the high strength LCP fibers. Consequently,the inflatable members of the invention have high hoop strength. Thehoop strength is typically about 1200 atm to about 2500 atm, andpreferably about 2000 atm. The burst pressure is about 14 atm to about27 atm, and preferably about 23 atm, and the tensile strength is about340 atm to about 1000 atm.

In a presently preferred embodiment, the inflatable member is formed byblow molding the extruded tube at 90° C. to 200° C., and 50 psi to 400psi, depending on the thermoplastic material used. The extrusion processresults in uniaxially oriented LCP fibers, and the blowing processimparts some radial orientation to the LCP fibers. Alternatively, arotating die and/or mandrel extrusion can be used to produce anextrudate having fibers with longitudinal and radial orientation. Thestrength of the inflatable member is related to the longitudinal andradial orientation of the LCP fibers, and the extent of orientationshould be tailored to ensure that the inflatable members produced willnot have radial failure during use.

High strength inflatable members of the invention provide increasedprotection against the risk of bursting during pressurization, and canbe used to produce strong, thin walled inflatable members. In anexpanded state, the inflatable member outer diameter is generally about0.1 cm to about 6 cm, and the length is about 10 mm to about 50 mm, andpreferably about 20 mm.

A variety of suitable thermoplastic polymers may be used for thenon-liquid crystal polymeric matrix in the LCP polymeric blend. Theoverall softness of the inflatable member can be improved by using softthermoplastic elastomers or polyolefins. Alternatively, stifferengineering polymers may be used as the matrix polymer. Presentlypreferred matrix polymers are polyether block amides such as PEBAX, andpolyamides such as nylon 12. Suitable thermoplastic polymers include,but are not limited to, PET, PEEK, PEN, Nylon, HYTREL, VESTAMID, PPS,and polyethylene.

The liquid crystal polymeric material is a separate phase from the nonliquid crystal polymeric material of the blend. Suitable liquid crystalpolymeric materials are copolyesters, such as those sold under the tradename VECTRA, and polyesteramides such as XYDAR. In a presently preferredembodiment the invention, the liquid crystal polymeric material andmatrix polymeric material are temperature-melt (T-melt) compatible, sothat the polymers melt in the same temperature range. The T-meltcompatibility is desirable because it avoids the polymer degradationthat may otherwise result during extrusion.

In another embodiment, the blend may contain a small fraction of acompatibilizer to improve the adhesion between the LCP and thethermoplastic material, including ionomers such as metal neutralizedsulfonated polystyrene, or polypropylene with maleic anhydride.

The length of the dilatation catheter 10 may be about 120 to about 150cm in length, and typically is about 135 cm in length. The outer tubularmember 14 has an OD of about 0.03 to about 0.05 inch (0.76-1.27 mm) andan ID of about 0.025 to about 0.035 inch (0.635-0.899 mm). The outertubular member 14 may taper in its distal portion to a smaller OD ofabout 0.04 to about 0.02 inch (1.02-10.55 mm) and a smaller ID of about0.03 to about 0.015 inch (0.762-0.381). The smaller diameter portionbetween the taper and the proximal extremity of the inflatable member 12may be about 5 to about 25 cm in length.

The inner tubular member 15 has an OD ranging from about 0.018 to about0.026 inch (0.457-0.66 mm), and the ID of the inner tubular member willusually be determined by the diameter of the guidewire 18 which is to beused with the catheter, which may range from about 0.008 to about 0.02inch (0.203-0.51 mm). The inner diameter of the inner lumen should beabout 0.002 to about 0.005 inch (0.051-0.127 mm) larger than the OD ofthe guidewire 18 to be used. Usually there will be a family of cathetersfor each size of guidewire with a variety of maximum inflated inflatablemember sizes, e.g., 0.5 to about 4 mm in diameter and with variousworking lengths ranging from about 1 to about 10 cm.

To the extent not previously described herein, the various cathetercomponents may be formed of conventional materials. For example,radiopaque marker 31 may be a gold band and the adapter body may beformed of polycarbonate polymers.

While the present invention has been described in terms of certainpreferred embodiments, those skilled in the art will recognize thatmodifications and improvements may be made to the invention withoutdeparting from the scope thereof. For example, while the catheterillustrated has an outer tubular member with proximal and distalsections, and an inner tubular member, a variety of suitable shaftdesigns may be used including a dual lumen shaft.

What is claimed is:
 1. A balloon catheter, comprising: a) a cathetershaft having a proximal end, a distal end, and at least one lumentherein; b) an inflatable member on a distal portion of the cathetershaft, which has an interior in fluid communication with the lumenwithin the shaft, and which is formed of a blend comprising a majoramount of non-liquid crystal polymeric material and a minor amount ofliquid crystal polymeric material existing as elongated liquid crystalpolymeric fibers having an aspect ratio of not less than about
 50. 2.The catheter of claim 1 wherein the inflatable member has a workinglength of about 10 mm to about 50 mm.
 3. The catheter of claim 1 whereinthe inflatable member has a burst pressure of about 14 atm to about 27atm.
 4. The catheter of claim 1 wherein the inflatable member has a hoopstrength of about 1200 atm to about 2500 atm.
 5. The catheter of claim 1wherein the liquid crystal polymeric material is less than about 10weight percent of the blend.
 6. The catheter of claim 1 wherein the nonliquid crystal polymeric material is a thermoplastic polymer selectedfrom the group consisting of polyolefins, polyamides, nylon,polyethylene-terephthalate, polyetheretherketone, polyether block amide,polyester block copolymers, polyethylene, polyphenylene sulfide, andpolyethylene naphthalate.
 7. The catheter of claim 6 wherein the blendincludes a compatibilizer for the liquid crystal polymeric material andthe thermoplastic polymer.
 8. The catheter of claim 7 wherein thecompatibilizer is selected from the group consisting of metalneutralized sulfonated polystyrene and polypropylene with maleicanhydride.
 9. The catheter of claim 1 wherein the aspect ratio is about80 to about
 100. 10. The catheter of claim 1 wherein the aspect ratio isgreater than
 100. 11. The catheter of claim 1 wherein the liquid crystalpolymeric material is about 20 weight percent of the blend.
 12. Aninflatable member for a catheter, the inflatable member being formed ofa blend comprising a major amount of non-liquid crystal polymericmaterial and a minor amount of liquid crystal polymeric materialexisting as elongated liquid crystal polymeric fibers having an aspectratio of not less than about 50, and being formed from a processcomprising extruding the blend at a draw down ratio of not less thanabout 3 to form an extruded tube having the liquid crystal polymericelongated fibers having an aspect ratio of not less than about 50, andradially expanding the tube to form the inflatable member.